Metal forming devices and method using magnetic and hydraulic pressure



Jan. 26, 1965 H. P. F URTH METAL. FORMING DEVICES AND METHOD USINGMAGNETIC AND HYDRAULIC PRESSURE Filed April- 11 1962 INVENTOR. J/A'AfllpREIT/1 United States Patent 0 3,167,043 METAL FORMINGDEVICES AND METHODUSING MAGNETIC AND HYDRAULIC PRESSURE Harold P. Forth, Berkeley, Calif.,assigner to Advanced Kinetics, Inc Costa -Mesa, Uaiih, a corporation ofCalifornia Filed Apr. 11, 1962, Ser. No. 186,785 8 Claims. (Cl. 113-44The present invention relates generally to metal forming by hydraulicpressure, and more particularly to devices and methods where metal isformed by a hydraulic pressure that is generated by exerting magneticpressure against a conducting diaphragm.

A sheet-metalwork piece and die immersed in a fluid can be subjected tohigh transient hydraulic pressure, forming the metal against the die.This pressure is usually generated by detonation of an explosiveimmersed in the fluid, or by a discharge of electric current through awire immersed in the fluid or through a small region of the fluid itselfbetween electrodes. Generating pressure by creating an explosion in thefluid creates an uncontrollable pressure wave commencing from the pointof explosion. The magnitude and duration of the pressure wave are beyondthe operators control seriously affecting the efliciency and quality ofthe forming process. Generally, pressure by the electric currentdischarge method is likewise uncontrollable, ineflicient, and of poorreliability. The electrodes erode and must be replaced for eachoperation. Accordingly it is an object of this invention to provide ahydraulic metal forming device of improved efiiciency and reliability.

The device of the present invention provides a device and method forforming metal, wherein hydraulic pressure is generated by the rapiddisplacement of a diaphragm immersed in the fluid, the diaphragm beingdisplaced by magnetic pressure.

Utilizing magnetic pressure which can be generated with precise controlof magnitude and duration, a device is provided which permits thegeneration of a pressure wave within a fluid of predetermined shape,magnitude, and duration within precise limits not available within theknown art. Efliciency, reliability, and quality of operation areachieved to a high degree because of the control achieved over themagnetic pressure pulse which generates the pressure shock waves in thefluid.

It is therefore another object of this invention to provide a hydraulicmetal forming device in which the pressure waves in the fluid can becontrolled in shape, magnitude, and duration.

It is a further object of this invention to provide a hydraulic metalforming device of improved elficiency, quality, and reliability.

Other objects and advantages of the present invention will becomeapparent from the following description and appended claims.

In the drawings:

FIGURE 1 is a schematic view of an immersible device for generatingpressure waves in a fluid by magnetic means. FIGURE 1A is a sectionalview of the device, forming tank, work, and die. FIGURE 1B is aperspective view of the pressure-wavegenerating device.

FIGURE 2 is a schematic view of a device, mounted on one side of aforming tank, for increasing the pressure of the fluid enclosed in thetank by magnetic means. FIGURE 2A is a sectional View of the device,forming tank, work, and die. FIGURE 2B is a perspective view of thedevice and forming tank.

According to a principal aspect of the invention a metal work piece andassociated die are immersed in a pressure transmitting fluid within aforming tank. A flexible diaphragm is positioned in the tank parallel toand adjacent the work piece. Means are provided for generatingmag neticpressure on the diaphragm whereby the diaphragm is displaced within thefluid to produce pressure shock waves which are transmitted to t-he workpiece. In this way the work piece may be formed against the die.

In order to form a metal workpiece efliciently by hydraulic means,hydraulic pressure in the working fluid may be generated either bydisplacing a diaphragm rapidly through the fluid, thus generating apressure Wave, 'or else by reducing the volume of the forming tank bymeans of a flexible diaphragm in a wall of the tank, thus giving rise toan increasing pressure of the fluid in the tank. In either case, thedisplacement of the diaphragm can be accomplished as rapidly andefliciently as desired by making the diaphragm of a conducting materialand applying magnetic pressure against it.

Magnetic pressure may be applied to a conducting diaphragm by setting upa transient magnetic field in such a manner that the spatial extent ofthe magnetic field is limited by the diaphragm. For example, if a coilis held near the diaphragm and a pulsed magnetic field is generated bypulsing current through the coil, the magnetic field is prevented frompenetrating through the diaphragm by eddy currents that are inducedtherein. There results a magnetic pressure.

P=B /81r against the diaphragm, where B is the strength of themagneticfield. The most efiicient means of applying magnetic pressure is topassa current directly along the dia phragm and return it by means of aplane return con ductor tha-tis nearly parallel to the diaphragm andclose to it. In that case the magnetic field extends over the leastvolume possible, and thereby the energy requirement for setting up themagnetic field is minimized. Particularly if the discharge time of thecapacitor bank that produces the magnetic field is short compared to theduration of the forming process, nearly perfect overall efficiency canbe achieved for the forming process.

The advantages of the present invention are the following. As in otherhydraulic forming devices and methods, a work piece of arbitrary shapecan be formed with highly uniform pressure in a standard forming tank,thus avoiding the need to make a specially designed form ing head foreach different forming operation. As in other devices and methods usingmagnetic pressure, the duration and strength of the pressure pulse canbe closely and conveniently controlled, and the efficiency can be madevery high. By comparison, the direct passage of current through theworking fluid is an ineflicient and poorly controllablepressure-generating method, since the heating, vaporizationxandionization of the fluid plays an essential role. The present inventionalso avoids the use of electrodes, w-hich tend to erode and must bereplaced at frequent intervals, and avoids the use of wires that aresometimes exploded electrically in the fluid, and that must be replacedfor each forming operation. The present in vention, like otherelectrically powered hydraulic form ing methods, has the advantage 'overforming methods using explosives that safety of the operating personnelis greatly increased and that high repetition rates of. the formingoperation are more easily achieved.

Referring now to the drawings:

In the forming device shown in FIGURE 1, a flexible metal diaphragm 11is attached to a metal backing plate 12, and a current indicated by thearrows 13 is passed along the backing plate and along the diaphragm. Amagnetic field then appears inside the loop formed by the backing plateand diaphragm, and interacts with the current in the diaphragm 11 todisplace the diaphragm 11 away from the backing plate 12. The pulsedcurrent is generated by a capacitor bank 14, which is discharged by aswitch 15. An auxiliary switch may be used to short circuit thecapacitor bank after discharge, if it is desired to avoid ringing of thecurrent. The clamping plate 16 holds the upper part of the diaphragm lllagainst the backing plate 12, thus restricting the motion of thediaphragm to its lower part. The upper part of the diaphragm 11 is madewider and is clamped closely against the backing plate 12, so as tominimize the volume of stray magnetic field. The backing plate 12 anddiaphragm 11 both have an electrically insulating coating or sleeve 33,to prevent electrical short-circuiting from one to th other, directly orthrough the working fluid. The assembly is clamped together by theinsulated draw-bolts 17. The forming tank 18 is filled with a suitablefluid l9, usually water, into which is immersed the work piece 29 andthe die 21, the space between them being void of fluid and usuallyevacuated. The diaphragm ill is placed near the work piece 20 andparallel to it, so that the pressure wave generated in the working fluid19 by the displacement of the diaphragm 11 will transfer energyefliciently to the work 20. The velocity of displacement of thediaphragm 11 is usually made comparable to the speed of sound in thefluid, so that negligible energy is lost by the flow of fluid into thespace between the diaphragm 11 and the backing plate 12, which wouldpermit relaxation of the fluid pressure without performance of thedesired work.

In the forming device shown in FIGURE 2, a closed metal forming tank 22is filled with fluid The flexible metal diaphragm 24 covers a window inthe tank 22 and is connected to the tank both physically andelectrically on all sides. A backing plate 25 is placed close to thediaphragm and parallel to it. One end of the backing plate 25 makesphysical and electrical contact with the tank at one end of the windowthat is covered by the diaphragm 24. A current indicated by the arrows26 is passed around the loop made by the backing plate 25, the diaphragm26 and the return conductor 27. A magnetic field is therefore set up inthis loop, and the resultant pressure on the diaphragm, which is strongonly in the central region of the diaphragm covered by the backingplate, displaces the central portion of the diaphragm. Electricalinsulation 34 is provided between the diaphragm and the backing plateand return conductor. The current pulse is drawn from the capacitor bank28 by closing the switch 29. An auxiliary switch may be used toshort-circuit the capacitor bank after discharge if it is desired toavoid ringing of the current. The work piece 30 and die 31 are immersedin the fluid 23, the space between the work and die being void of fluidand usually evacuated. The displacement of the diaphragm reduces thevolume enclosed by the tank and exerts pressure onthe fluid. The fluidin turn does the work of forming the work piece against the die. Sincethe compressed fluid cannot escape from the tank, the displacement ofthe diaphragm need not occur at a velocity comparable to the velocity ofsound in the fluid, and

the work need not be located near the diaphragm or be speciallyoriented.

v The principles of the devices in FIGURES l and 2 can be combined inseveral ways. The device of FIG- URE 1 can be mounted against aconducting wall of the forming tank, the wall being used as the backingplate. Alternatively a device with a sealed diaphragm, like the deviceof FIGURE 2, can be used for immersion into a tank.

Various of the novel features of the present invention are set forth inthe following claims.

I claim: a

1. A hydraulic metal forming device comprising,

a forming tank,

a work piece in said tank,

a die' adajcent said work piece,

the space between said work piece and said die being evacuated,

an electrically conductive flexible diaphragm in said tank parallel tosaid work piece,

a high energy current source,

a conductor in said tank responsively connected to said current sourceand shaped to provide a magnetic field of predetermined strength,

said flexible diaphragm positioned within said magnetic field at apredetermined distance from said conductor,

means for providing a flow of current through said flexible diaphragm,

the current flowing in said conductor generating said magnetic field andthe current flowing in said diaphragm interacting with said magneticfield to provide magnetic pressure on said diaphragm,

the magnetic pressure on said diaphragm causing said diaphragm todisplace the fluid in said tank whereby pressure waves are transmittedthrough said fluid to form said work piece against said die.

2. The device recited in claim 1 wherein said conductor is conductivelyconnected to said diaphragm to cause current to flow in said diaphragm.

3. In a hydraulic metal forming device wherein a work means forproviding a current path through said diaphragm, the current flowing insaid plate generating said magetic field and the current flowing in saiddiaphragm interacting with said magnetic field to provide magneticpressure on said diaphragm,

whereby the flexible end of said diaphragm displaces said fluid creatingpressure waves which are transmitted through said fluid to form saidwork piece. 4. The device of claim 3 wherein said means for providing acurrent path through said diaphragm includes means for conductivelyconnecting the lower end of said diaphragm to said plate and may beelectrically insulating the upper end of said diaphragm for said plate,the upper end of said diaphragm being responsively connected to saidcurrent source whereby a current path is provided for said currentsource through said plate and said diaphragm.

5. The device of claim 3 wherein said tank is close and wherein there isprovided a window in said tank, said diaphragm positioned to cover saidwindow, whereby the flexible end of said diaphragm compresses saidfluid.

6. The device of claim 3 wherein theupper portions of said backing plateand said diaphragm are wide compared to the narrow lower portions ofsaid backing plate and said diaphragm.

7. In a hydraulic metal forming device wherein a work piece is formedagainst a die in a closed tank containing a fluid for transmittingpressure to form said work piece, the improvement comprising, a wind atone end of said tank, an electrically conductive diaphragm in said tankhaving its ends attached to said tank to cover said window,

means for generating magnetic pressure against said diaphragm, wherebysaid diaphragm displaces the fluid in said closed container to compressthe fluid and form said work piece.

8. In a device for forming a metal work piece by hydraulic pressure,

a forming tank a pressure transmitting fluid in said tank,

relation with said work piece,

means for producing pressure shock waves through said fluid to form saidWork piece against said die comprising,

a flexible electrically conductive metallic diaphragm in said tankparallel to and adjacent to said work piece,

and means for applying pressure on said diaphragm whereby said diaphragmis displaced Within said fluid to produce said pressure shock waves,said pressure applying means comprising,

a transmission line responsively connected to a current source andhaving a portion shaped to provide a magnetic field of high strength,

said diaphragm positioned within said magnetic field at a predetermineddistance from said transmission line,

and means for providing a flow of current in said diaphragm,

References Cited by the Examiner UNITED STATES PATENTS 2,559,227 7/ 5 1Rieber 128-24 2,648,125 8/53 McKenna et al 264-84 2,976,907 3/61 Harveyet a1 153-10 2,983,242 5/61 Cole 113-44 3,121,211 2/64 Eskin et a1.346-8 15 MICHAEL V. ERINDESE, Primary Examiner.

WZLLIAM I. STEPHENSGN, Examiner.

8. IN A DEVICE FOR FORMING A METAL WORK PIECE BY HYDRAULIC PRESSURE, AFORMING TANK A PRESSURE TRANSMITTING FLUID IN SAID TANK, A DIEPOSITIONED IN SAID TANK ADJACENT TO AND IN FORMING RELATION WITH SAIDWORK PIECE, MEANS FOR PRODUCING PRESSURE SHOCK WAVERS THROUGH SAID FLUIDTO FORM SAID WORK PIECE AGAINST SAID DIE COMPRISING, A FLEXIBLEELECTRICALLY CONDUCTIVE METALLIC DIAPHRAGM IN SAID TANK PARALLEL TO ANDADJACENT TO SAID WORK PIECE, AND MEANS FOR APPLYING PRESSURE ON SAIDDIAPHRAGM WHEREBY SAID DIAPHRAGM IS DISPLACED WITHIN SAID FLUID TOPRODUCE SAID PRESSURE SHOCK WAVES, SAID PRESSURE APPLYING MEANSCOMPRISING, A TRANSMISSION LINE RESPONSIVELY CONNECTED TO A CURRENTSOURCE AND HAVING A PORTION SHAPED TO PROVIDE A MAGNETIC FIELD OF HIGHSTRENGTH, SAID DIAPHRAGM POSITIONED WITHIN SAID MAGNETIC FIELD AT APREDETERMINED DISTANCE FROM SAID TRANSMISSION LINE, AND MEANS FORPROVIDING A FLOW OF CURRENT IN SAID DIAPHRAGM, THE CURRENT FLOWING INSAID TRANSMISSION LINE GENERATING SAID MAGNETIC FIELD AND THE CURRENTFLOWING IN SAID DIAPHRAGM INTERACTING WITH SAID MAGNETIC FIELD TOPROVIDE MAGNETIC PRESSURE ON SAID DIAPHRAGM.